1. Technical Field
The present invention relates to a light emitting device, and more particularly to a light emitting diode (LED) light bulb.
2. Related Art
Compared with a conventional incandescent light bulb, an LED, when being in use, is capable of generating light of high brightness and only consumes little electric energy. Furthermore, the LED has advantages of low driving voltage, high response speed and long life time. Therefore, LEDs are widely used for replacing lighting devices such as fluorescent lamps, ceiling lamps, search lights, down lamps and conventional light bulbs.
Generally, an LED light bulb is designed to mainly include a heat-dissipating body on which a pedestal and a connection base are disposed. The pedestal is provided with a circuit board, and a plurality of LEDs are disposed on the circuit board by a surface mounting technology (SMT), and then, a bulb-shaped lampshade is disposed on the pedestal for covering the plurality of LEDs, so as to form a light bulb structure. A drive circuit electrically connected to the LEDs is disposed inside the connection base, and the out surface of the connection base has a spiral conductive portion. The spiral conductive portion is used for being fastened to a lamp socket, so as to be electrically connected to an external power supply, and, therefore a power supply can transfer the electricity through the conductive portion and the drive circuit to the LEDs.
In operation, the great deal of heat generated by the LED would accumulate in the circuit board, overheat the LED and, therefore, cause problems such as significant light attenuation, decrement of life time and reducing efficiency. To prevent such problems, a usual way is to dispose a plurality of heat dissipation fins on the heat-dissipating body. The heat dissipation fins surround the surface of the heat-dissipating body, and a gap exists between two adjacent heat dissipation fins. Such gaps are used as a heat-dissipating channel for air circulation. Furthermore, in order to increase the surface area of the heat dissipation fins for dissipating heat, usually a considerable number of heat dissipation fins are arranged on the heat-dissipating body, and the side edge of the heat dissipation fin having a smaller contact area is connected to the heat-dissipating body. Accordingly, the heat dissipation fins have larger surface areas in the heat-dissipating channel for heat exchange.
However, as the number of the heat dissipation fins increases, the width of the heat-dissipating channel becomes narrower, so that the heat cannot be removed to the external environment due to poor heat convection. As a result, the heat-dissipating efficiency of the heat-dissipating body is reduced, or even worse, the heat-dissipating body loses the heat-dissipating ability.
Currently, in the LED light bulb provided with the heat dissipation fins, in order to effectively cool the bulb, a recess is usually formed on the surface of the heat-dissipating body, and the heat dissipation fins are annularly disposed on the outer surface of the heat-dissipating body and corresponding to the recess. The lampshade is engaged in the recess, and only an upper surface of the lampshade is exposed outside the heat-dissipating body. Accordingly, the light generated by the LED can be projected to the external environment through the lampshade; and the lampshade is surrounded by the heat dissipation fins, so that a better heat-dissipating effect is provided. Although such configuration can improve the heat-dissipating efficiency, the light is blocked by the inner wall surface of the recess after penetrating the lampshade. Therefore, the LED light bulb only has an output light profile in which light is output substantially in a single direction and is not suitable for being applied to a lighting apparatus with a wide illuminating angle.
In another kind of LED light bulb, in order to provide an output light profile of a wide illuminating angle (such as, a 120-degree angle), the circuit board and the LEDs are disposed on the surface of the heat-dissipating body, and the heat dissipation fins are disposed on the side surface of the heat-dissipating body adjacent to the circuit board. Therefore, when the LEDs and the circuit board are covered by the lampshade, the lampshade is located at the surface of the heat-dissipating body, and the heat dissipation fins surround the outer periphery of the heat-dissipating body and are located below the lampshade, so as to prevent the heat dissipation fins from covering the lower edge surface of the lampshade and causing interference to the output light profile of the LED light bulb. Although this kind of LED light bulb can have an output light profile with about a 120-degree angle, the heat dissipation fins cannot directly dissipate heat from the surface of the lampshade and therefore, the heat-dissipating ability is limited.
In the LED light bulbs in the prior art, no matter which configuration is adopted for the heat dissipation fins, the light bulb structure formed thereby only has a single output light profile. Therefore, the output light profile of the LED light bulb cannot be adjusted according to requirements in use, so that the application of the LED light bulb to different lighting apparatuses is greatly limited.